U.S. Pat. No. 4,485,297 discloses an electrical heating device in which a semi-conductor pattern is printed on an insulating substrate. The pattern includes a pair of parallel longitudinal stripes and a plurality of bars extending obliquely between the stripes. The heating device is designed to produce a uniform watt density over the heated area, and the patent teaches that the watt density may be varied by changing the oblique angle between the bars and stripes.
U.S. Pat. No. 4,633,068, discloses a heating device, particularly suited for use as an infrared imaging target, which similarly includes a semi-conductor pattern including a plurality of bars extending between a pair of longitudinally-extending stripes. Different areas of the device there disclosed have different watt densities, the variation in watt density between the different areas being accomplished by varying the width of selected bars along their length.
U.S. Pat. No. 4,542,285 discloses conductors useful for connection to semi-conductor pattern of devices such as those in the above-referenced patent and application. The conductor comprises a conductive metal strip having a pair of transversely-spaced, longitudinally-extending strip portions and, therebetween, a central portion that includes a plurality of longitudinally-spaced openings. As disclosed, one of the conductor's strip portions overlies a stripe of the semi-conductor pattern, and an overlying insulating layer is sealed to the layer carrying the semi-conductor pattern through the openings in the central portion and along the inner and outer edges of the conductor.
The above identified U.S. Patents are hereby incorporated by reference.